1. Field of the Invention
The present invention generally relates to a range switching device that is applied to an automatic transmission installed in a vehicle and is used for switching between ranges according to an operation performed by the driver of the vehicle, the ranges including a park (P) range, a neutral (N) range, a drive (D) range, and a reverse (R) range. The present invention specifically relates to a range switching device that uses a shift-by-wire method by which the operation performed by the driver of the vehicle is transmitted via an electric signal.
2. Description of the Related Art
Conventional examples of range switching devices using the shift-by-wire method include a range switching device that transmits an operation of the driver of the vehicle to solenoid valves via an electric signal and that switches a range switching valve by operating the solenoid valves in this manner.
It has been proposed to configure such a range switching device so as to have a fail-safe function so that, in the case where all the solenoid valves go into an unenergized state due to a discontinuation of the electric power supply or the like, the range switching device maintains a parking release state as well as the drive (D) range state until the engine is stopped (see Japanese Patent Application Publication No. JP-A-2002-533631).
In the case where all the solenoid valves go into an unenergized state while the vehicle is in the drive (D) range, the range switching device disclosed in Japanese Patent Application Publication No. JP-A-2002-533631 is able to maintain the parking release state until the engine is stopped. However, in the case where all the solenoid valves go into an unenergized state while the vehicle is in the neutral (N) range or the reverse (R) range, the range switching device disclosed in JP-A-2002-533631 has a problem in that it switches the vehicle into the parking state.